EBM: Systematic Review & MetaMeta--analysis analysis · EBM: Systematic Review & MetaMeta--analysis...
Transcript of EBM: Systematic Review & MetaMeta--analysis analysis · EBM: Systematic Review & MetaMeta--analysis...
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EBM:EBM:
Systematic Review & Systematic Review &
MetaMeta--analysisanalysis
RAID433: Critical Thinking in Medicine
Section for Clinical Epidemiology & Biostatistics
Faculty of Medicine Ramathibodi Hospital
v. 2
Scope of lectureScope of lecture
• Systematic review and traditional review
• Methods of conducting systematic review
• Meta-analysisPublication bias
• Critical appraisal of systematic review and meta-analysis
• Validity
• Result from systematic review
• Applicability
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Trends towards Systematic ReviewTrends towards Systematic Review
There have been more than 400 systematic reviews and meta-analyses published in
the discipline of nephrology since 1990, with the annual number increasing with time.
Garg A X et al. CJASN 2008;3:253-260
Hierarchy of EvidenceHierarchy of Evidence
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• Primary analysis (Primary research): Original studies• Original analysis of research data
• Secondary analysis (Secondary research)• Re-analysis of the original data either using another
statistical technique or answering new questions with previously obtained data
Traditional “narrative review” articlesTraditional “narrative review” articles
• Qualitative
• Summary of all primary research on a given topic
• May provide good background information
• Major disadvantages:
• Subjective, unsystematic approach
• May be biased from author who may be very selective of the articles chosen for review
• Conflicting of evidences
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What is “Systematic Review”What is “Systematic Review”
• A review of a particular subject undertaken in such a systematic way that risk of bias is reduced.
• Systemic reviews have explicit, scientific, and comprehensive descriptions of their objectives and methods.
Hunink, Glasziou et al, 2001.
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Systematic review
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Systematic Review vs Narrative ReviewSystematic Review vs Narrative Review
Characteristic Narrative Review Systematic Review
Clinical question Seldom reported, or
address several questions
Focused question: PICO
Search for primary articles
Seldom reported, not comprehensive
Comprehensive search of several sources
Selection of primary articles
Seldom reported,often biased
Explicit inclusion and exclusion criteria
Evaluation of quality of primary studies
Seldom reported, not usually systematic
Methodological quality
of primary articles is assessed
Summary of results of primary studies
Usually qualitative, nonsystematic
Synthesis is systematic, meta-analysis
Conducting Systematic ReviewConducting Systematic Review
1. Define question
2. Conduct literature search
3. Apply inclusion and exclusion criteria
4. Create data abstraction
5. Conduct analysis
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11. Define question. Define question
• Specify inclusion and exclusion criteria• Population
• Intervention/Exposure
• Outcome
• Methodology (time, language, publication restriction)
22. Conduct literature search. Conduct literature search
• Decide on information source• Databases
• Experts
• Funding agencies, pharmaceutical companies
• Hand searching
• Trial registries
• Cochrane database of randomized controlled trials
• Citation lists of retrieved articles (Cross-references)
• Identify titles and abstract
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Literature searchLiterature search
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33. Apply inclusion and exclusion. Apply inclusion and exclusion
• Apply inclusion and exclusion criteria to titles and abstracts
• Obtain full articles to eligible titles and abstracts
• Apply inclusion and exclusion criteria to full articles
• Select final eligible articles
• Assess agreement on study selection
Inclusion and ExclusionInclusion and Exclusion
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44. Create data abstraction. Create data abstraction
• Data abstraction• Participants, Interventions, Comparison interventions,
study design
• Result
• Methodologic quality
• Assess agreement on validity assessment
Data Collecting FormsData Collecting Forms
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55. Conduct analysis. Conduct analysis
• Determine method of generating pooled estimates across studies
• Generate pooled estimates (if appropriate)
• Explore heterogeneity
• Conduct subgroup analysis if appropriate
• Explore possibility of publication bias
MetaMeta--analysisanalysis
• “The analysis of analyses”
• Statistical techniques for merging and contrasting results across studies
• Synthesis of pooled effect
• Giving greater weight to studies with• Less variance (V)
• More precision (W)
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Systematic review and MetaSystematic review and Meta--analysisanalysis
• Systematic review does not necessarily contain meta-analysis
• Identified no or too little studies
• Identified studies with different methods or different outcomes that is not reasonable to combine the effect
• Meta-analysis also does not need to be done from systematic review
• You can do meta-analysis with specific studies selection
• But it is best to be done together.
Process of MetaProcess of Meta--analysisanalysis
• Pooling data• Proportion: Incidence rate, Prevalence
• Mean: Mean, Mean difference, Standardized Mean Difference
• Ratios: Relative risks, Odds ratio, Risk difference
• Diagnostic performances: Sensitivity/Specificity
• Etc.
• Subgroup analysis
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Prevalence, RR, OR revisitedPrevalence, RR, OR revisited
Disease (Outcome)
Develop disease (+)
No disease (-)
Exp
osu
re
Have
exposure (+)
A B
Do not
have
exposure (-)
C D
Forest PlotForest Plot
• Plot of effect size and their precision
• Most common way to report result in meta-analysis
• Help identify patterns of effect
• Can spot outliers
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Forest plot of the effects of alpha-blockers on treatment
responsiveness; random effect model
Overall (I-squared = 64.2%, p = 0.016)
Cheah P.Y. (2003)
Tugcu V. (2007)
Mehik A. (2003)
Nickel J.C. (2004)
Nickel J.C. (2008)
Alexander R.B. (2004)
Author (year)
1.57 (1.07, 2.30)
1.63 (1.03, 2.57)
2.00 (1.14, 3.52)
3.82 (1.53, 9.55)
2.00 (0.76, 5.23)
1.00 (0.79, 1.27)
1.09 (0.54, 2.21)
RR (95% CI)
100.00
20.53
17.74
10.87
10.20
26.10
14.56
26
20
13
9
68
12
R
17
10
4
18
70
33
NR
16
10
4
5
66
11
R
27
20
16
25
68
34
NR
1.57 (1.07, 2.30)
1.63 (1.03, 2.57)
2.00 (1.14, 3.52)
3.82 (1.53, 9.55)
2.00 (0.76, 5.23)
1.00 (0.79, 1.27)
1.09 (0.54, 2.21)
RR (95% CI)
100.00
20.53
17.74
10.87
10.20
26.10
14.56
%weight
Alpha Placebo
1.2 .5 1 1.57 5 10
Risk Ratio
Fixed Effect Model vs. Random Effects ModelFixed Effect Model vs. Random Effects Model
• These are two mathematical methods for deriving a pool estimation
• Fixed effect model• Assumption: single common (“fixed”) result
• If every study were infinitely large, they would yield an identical result
• No statistical heterogeneity among studies
• Random effect model• Assumption: individual studies are estimating different
treatment effects (distribution with some central value and some degree of variability)
• We interested in the central value and distribution of effect
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Fixed Effect Model Random Effect Model
Underlying assumption All trials estimate the same effect
Varying underlying effect
Computational method
Error term comes from
“within trial” (ignore
between-study variability)
Error term comes from
“within trial” and “between trial”
Practicalconsequences
Narrower confidence interval
Wider confidence interval
HeterogeneityHeterogeneity
• Cochrane’s Q Test
• Higgin’s I2
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Cochrane’s Q testCochrane’s Q test
Cochrane’s Q testCochrane’s Q test
• Null hypothesis: underlying effect is the same
• Generate p value to test the null hypothesis
• p value = probability to accept null hypothesis
• Low p value: random error is an unlikely explanation of the difference between studies (therefore, there may be some systematic error or bias)
• High p value: underlying assumption of pooling holds true
kH θθθθ ==== ...: 3210
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kH θθθθ ==== ...: 3210
Cochrane’s Q testCochrane’s Q test
• This test is less sensitive when the number of studies is low (<25 studies).
• The level of significance is recommended to be at least 0.10.
Higgin’sHiggin’s II22
Higgins JP, Thompson SG, et.al. Measuring inconsistency in meta-analyses. BMJ 2003; 327 (7414): 557-60.
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One thing to consider…One thing to consider…
• Because systematic review searched databases of published studies
• Do you think we will get all information available?
• What will happen if we only choose studies that get published?
Publication Bias (Reporting Bias)Publication Bias (Reporting Bias)
• Publication bias and other related biases can be summarised as statistically significant, 'positive' results being:
• more likely to be published (publication bias)
• more likely to be published rapidly (time lag bias)
• more likely to be published in English (language bias)
• more likely to be published more than once (multiple publication bias)
• more likely to be cited by others (citation bias)
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Funnel Plot for assessing publication biasFunnel Plot for assessing publication bias
• Plot between log(effect size) and precision (1/variance)
• Assumption: all studies are estimating the same effect, so the estimated effects should be normally distributed about the unknown true effect
• The spread of estimated effect should therefore be proportional to their variances, just like a funnel
• Small study (lower n) – higher variance, more spread
• Large study (higher n) – lower variance, more narrow
1/variance
Ln(effect size)
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0
.1
.2
.3
.4
.5
Sta
ndard
err
or
-1 0 1 2ln(RR)
Studies
p < 1%
1% < p < 5%
p > 5%
Figure 5. Contour enhanced-funnel plot
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Sources of plot asymmetrySources of plot asymmetry
• Biased selection of study (Selection Bias)
• Heterogeneity of treatment effects
• Poor quality of research methods
• Publication bias
Critical Appraisal of Systematic ReviewCritical Appraisal of Systematic Review
1. Are the results valid?
2. What are the results?
3. How can I apply the results to patient care?
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11. Are the results valid?. Are the results valid?
• Did the review include explicit and appropriateeligibility criteria?
• Was biased selection and reporting of studies unlikely?
• Were the primary studies of high methodologicquality?
• Were assessments of studies reproducible?
11..1 1 Did the review include explicit and appropriate eligibility Did the review include explicit and appropriate eligibility
criteria?criteria?
• Too broad or too narrow review?
Consider these systematic review questions:
- All treatment modalities for all types of cancer to look for mortality
- All antiplatelet effect on all CV events
- Aspirin dose to prevent thrombotic stroke in patients who had TIA
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- All treatment modalities for all types of cancer to look for mortality (Obviously broad)
- All antiplatelet effect on all CV events (Still broad)
- Aspirin dose to prevent thrombotic stroke in patients who had TIA
Appropriate eligibility criteriaAppropriate eligibility criteria
• Results likely to be similar across range of patients? (older/younger, sicker/less sick)
• Results likely to be similar across range of intervention? (higher/lower dose, expert/non expert use)
• Results likely to be similar across range of outcome measured? (shorter/longer follow-up)
• Did it turn out that results were indeed similar across the range of patient, intervention, and outcome?
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Selecting articles that are most likely to provide valid resultsSelecting articles that are most likely to provide valid results
Therapy - Were patients randomized?- Was follow-up complete?
Diagnosis - Was the patient sample representative of those with
the disorder?
- Was the diagnosis verified using credible criteria that
were independent of the items of the medical history,
physical examination, lab tests, or imaging procedures under study?
Harm - Did the investigators demonstrate similarity in all
known determinants of outcome or adjust for
differences in the analysis?- Was follow-up sufficiently complete?
Prognosis - Was there a representative sample of patients?
- Was follow-up sufficiently complete?
11..2 2 Was the Search for Relevant Studies detailed and Was the Search for Relevant Studies detailed and
exhaustive?exhaustive?
• Complete, or at least a representative sample of the available eligible studies
• Bibliographic databases• MEDLINE
• EMBASE
• CINAHL
• Cochrane Central Register of Controlled Trials
• Personal contact
• Scientific meeting, doctoral thesis, ongoing trials by pharmaceutical companies
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• Reporting bias: mostly due to the failure to publish studies with negative results
• For unpublished studies, researchers should try to use:
• Full written reports
• Same eligibility criteria as other published reports
Individual patientIndividual patient--data metadata meta--analysisanalysis
• Use individual patient data in primary study, rather than reported data
• Strengthen the influence from a systematic review
• Can facilitate• True intention-to-treat analysis
• Subgroup analysis
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11..3 3 Were the primary studies of high Were the primary studies of high methodologicmethodologic quality?quality?
• Methodology• Study design
• Appraisal of quality• Quality scale: ex. JADAD scale
• Quality table (Cochrane’s risk of bias assessment)
• Quality of primary study is assessed using similar tool as you appraised primary study
JADAD ScaleJADAD Scale
Jadad AR, Moore RA, Carroll D,et al. Assessing the quality of reports of randomized clinical trials: is blinding necessary? Control Clin Trials 1996; 17:1–12.
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Cochrane’s Risk of Bias assessmentCochrane’s Risk of Bias assessment
Type of bias Description Relevant domains in the Collaboration’s
‘Risk of bias’ tool
Selection bias. Systematic differences between
baseline characteristics of the
groups that are compared.
•Sequence generation.
•Allocation concealment.
Performance bias. Systematic differences between
groups in the care that is
provided, or in exposure to factors
other than the interventions of
interest.
•Blinding of participants and personnel.
•Other potential threats to validity.
Detection bias. Systematic differences between
groups in how outcomes are
determined.
•Blinding of outcome assessment.
•Other potential threats to validity.
Attrition bias. Systematic differences between
groups in withdrawals from a
study.
•Incomplete outcome data
Reporting bias. Systematic differences between
reported and unreported findings.
•Selective outcome reporting
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11..4 4 Were Were assessments of studies reproducibleassessments of studies reproducible??
• Systematic reviews are subject to both mistakes (random error) and bias (systematic error)
• Having more than one reviewer guards against these errors
22. What are the results. What are the results
• Were the results similar from study to study?
• What are the overall results of the review?
• How precise were the results
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22..1 1 Were the results similar from study to study?Were the results similar from study to study?
• Visual evaluation of variability• How similar are the point estimates
• To what extent do confidence intervals overlap
• Statistical tests evaluating variability• Yes-or-no test for heterogeneity (p value)
• I2 test that quantifies the variability explained by between-study differences in results
Visual evaluation of variabilityVisual evaluation of variability
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Statistical testsStatistical tests
• Cochrane Q
• I2 test
22..2 2 What are the overall results of the reviewWhat are the overall results of the review
• Dichotomous outcome• Relative risk
• Odds ratio
• Continuous outcome• Mean different
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22..3 3 How precise were the resultsHow precise were the results
• Confidence interval around that estimate
33. How can I apply the results to patient care?. How can I apply the results to patient care?
• Were all patient-important outcomes considered?
• Are any postulated subgroup effects credible?
• What is the overall quality of the evidence?
• Are the benefits worth the costs and potential risks?
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33..1 1 Were all patientWere all patient--important outcomes considered?important outcomes considered?
• Adverse effects of therapy
• Costs
33..2 2 Are any postulated subgroup effects credible?Are any postulated subgroup effects credible?
• Subgroup analysis – playing with chance
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Guidelines for deciding whether apparent differences in Guidelines for deciding whether apparent differences in
subgroup response are realsubgroup response are real
• Did the hypothesis precede rather than follow the analysis?
• Was the subgroup difference one of a small number of hypothesized effects tested?
• Is the subgroup difference suggested by comparisons within rather than between studies?
• Is the magnitude of the subgroup difference large?
• Is the subgroup difference consistent across studies?
• Was the subgroup difference statistically significant?
• Does external evidence support the hypothesized subgroup difference?
33..3 3 What is the overall quality of the evidence?What is the overall quality of the evidence?
• What do you think about the overall quality?
• Do you believe in the results?
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33..4 4 Are the benefits worth the costs and potential risks?Are the benefits worth the costs and potential risks?
• Weight between costs/risks and benefits
• Do not forget patient preference and clinical expertise
Quality of therapeutic studiesQuality of therapeutic studies
• Clinical trials:A systematic study on pharmaceutical products in human subjects in order to discover or verify the effects of and/or identify any adverse reaction to investigational products, and/or to study the absorption, distribution, metabolism and excretion of the products with the objective of ascertaining their efficacy and safety.
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Phases of Clinical TrialPhases of Clinical Trial
Phase IClinical pharmacology / toxicology, dose
fining, safety, perfection of technique
Phase IIInitial clinical investigation for
treatment effect, pilot study
Phase IIIFull-scale evaluation of treatment effect
(efficacy)*
Phase IV Post-market surveillance (effectiveness)
Efficacy vs Effectiveness studyEfficacy vs Effectiveness study
• Efficacy: Does receiving treatment work under ideal conditions?
• Limit only to patients that will cooperate fully with medical advice
• Effectiveness: Does offering treatment help under ordinary circumstances?
• Offering treatment to patients and allowing them to accept or reject it as they might ordinarily do
• If a treatment is found to be ineffective:• Lack of efficacy
• Lack of patient acceptance
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sample
Population
RandomizationRandomization
Treatment Control
OutcomeNo
outcome OutcomeNo
outcome
Blind assessmentBlind assessment
Randomized Control Trial
EndBeginning
Study subjects
Intervention
Death
Alive
Control
Death
Alive
• Randomization• Concealment• Intention to treat
analysis• Similar prognosis
• Blinding• Patients• Clinicians• Outcome
assessors• Adequate follow -up
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Randomized AllocationRandomized Allocation
RandomisationRandomisation
• Allocation of individuals to groups by chance.
• Within the limits of chance variation, randomisationshould make the control and the experimental groups similar at the start of the investigation and ensure that personal judgment and prejudices of the investigator do not influence allocation
Randomized AllocationRandomized Allocation
RandomisationRandomisation
• All subjects in the sample have same probability of being assigned to the experimental or control group.
• Any underlying factors the may affect the outcome are equivalent for each group.
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Randomized controlled trials (RCT)Randomized controlled trials (RCT)
Populationof patientsWith the Condition Sample
Improved
Not improved
Improved
Not improved
Outcomes
Experimental
Comparison
Random sampling
R
Type of randomizationType of randomization
• Simple
• Block
• Stratified
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Simple (unrestricted) randomizationSimple (unrestricted) randomization
• Coin, dice (not preferred)
• May be biased
• Can not be audit by others
• Table of random numbers
• Computer generated
Block RandomizationBlock Randomization
Subject 1
Subject 2
Subject 3
Subject 4
Block 1
Subject 1
Subject 2
Subject 3
Subject 4
Subject 1
Subject 2
Subject 3
Subject 4
Block 2 Block J
R R R
A B A B A B
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Stratified allocationStratified allocation
• Example• Gender: Male or female
Male
Female
R
R
A
A
B
B
Allocation concealmentAllocation concealment
• Generation of an unpredictable randomized allocation sequence .
• It represents the first crucial element of randomization in a RCT.
• Allocation concealment refers to the technique used to implement the sequence, not to generate it.
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How to conceal?How to conceal?
• Local: Sequentially numbered, opaque envelopes
• Central: computer-based
• Emergency situation?
Treatment100
Control100
8/80 = 10%
20/100 = 20%
Intention to treat vs. Intention to treat vs. Per protocol Per protocol analysisanalysis
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Per protocolPer protocol
or Explanatory trialsor Explanatory trials
• “ Which experimental treatment itself is better?”
• Analysis according to the treatment each patient actually received, regardless of the treatment to which they were randomized
• Dissimilarities between groups
Treatment100
Control100
8/80 = 10%
20/100 = 20%
12/20 = 60%
Intention to treat vs. Intention to treat vs. Per protocol Per protocol analysisanalysis
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Intention to treat or management trialsIntention to treat or management trials
• “ Which treatment policy is best at the time the decision must be made?”
• Analysis according to the assigned group
• Increasing the chance of a negative study
Per protocol analysisPer protocol analysis
• Excluding noncompliant patients from the analysis leaves behind those who may be destined to have a better outcome.
• Destroys the unbiased comparison provided by randomization
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3 3 CC
• Compliance
• Contamination
• Co-intervention
Why blinding is important?Why blinding is important?
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Potential benefits of blinding Potential benefits of blinding
Individuals Potential benefits
Patients • Less likely to have biased psychological or physical
responses to intervention
• More likely to comply with trial regimens
• Less likely to seek additional adjunct interventions
Clinicians • Less likely to differentially administer co-interventions
• Less likely to differentially adjust dose
• Less likely to differentially withdraw participants
• Less likely to differentially encourage or discourage
participants to continue trial
Assessors • Less likely to have biases affect their outcome
assessments, especially with subjective outcomes of
interest
Placebo Placebo
• An inert medication or procedure.
• The placebo effect (usually but not necessarily beneficial) is attributable to the expectation that the regimen will have an effect.
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Comparison groupComparison group
• No intervention
• Placebo treatment
• Standard treatment
Outcome measurementOutcome measurement
Surrogate outcome
Low-density lipoprotein
(LDL)
Proteinuria
Clinical outcome
Death
ESRD
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Surrogate outcomeSurrogate outcome
• Laboratory or physiologic measurement used as a substitute for an outcome that measure directly
• A surrogate outcome will be consistently reliable only if there is a causal connection between change in surrogate and change in the clinically important outcome.
Composite outcomeComposite outcome
• Combination of multiple endpoints e.g. combined death, MI or stroke
• Frequently used as primary outcome measures in RCT
• Increased statistical efficiency
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What should you do when blinding is impossible?What should you do when blinding is impossible?
• Strict to treatment protocol: to prevent unequal co-intervention
• Equally intense follow-up of experimental and control patients.
• External outcome adjudicators: to reduce biased outcome measurement
MethodsMethods
What should they do?
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When does loss to followWhen does loss to follow--up seriously threaten validity?up seriously threaten validity?
Trial A Trial B
Treatment Control Treatment Control
No. of patients
randomized
1000 1000 1000 1000
No. of lost to
F/U
30 (3%) 30 (3%) 30 (3%) 30 (3%)
No. of death 200 (20%) 400 (40%) 30 (3%) 60 (6%)
RRR not
counting
patient lost to
F/U
0.2/0.4
= 0.50
0.03/0.06
= 0.50
RRR for worst-
case scenario
0.17/0.4
= 0.43
0.00/0.06
= 0
Treatment effectTreatment effect
Control Experimental ARR RRR RR
80 KG 60 KG 20 KG 25% 75%
My past
weight
My present
weight
The absolute
Weight I lost
The percent
weight I lost
The percent
weight that
remained
Rc Rt Rc-Rt (Rc-Rt)/Rc Rt/Rc
My past risk My present risk The absolute
risk I lost
The percent
risk I lost
The percent
risk
remaining
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How large was the treatment effectHow large was the treatment effect??
Incidence of contrast
nephropathy
Absolute Risk
Reduction
ARR
Relative Risk
Reduction
RRR
Number
Needed to
Treat
NNT
Hydration
Control
Event
Rate
CER
NAC
Experimental
Event
Rate
EER
CER - EERCER - EER
CER 1/ARR
9.6% 2.8%
0.10-0.05
= 0.05
= 5%
(0.10-0.05)/0.10
= 0.5
= 50%
Confidence IntervalsConfidence Intervals
-50 -25 0 25 50 75
Relative risk reduction(%)
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Number needed to treat (NNT)Number needed to treat (NNT)
Number needed to harm (NNH)Number needed to harm (NNH)
Number needed to treat (NNT)
• Number needed to be treated to prevent one more event
NNT = 1/ (Riskcontrol-Risktreatment)
= 1/ARR
Number needed to harm (NNH)
• Number needed to be treated to harm one more of them
NNH = 1/ (Rtreatment-Rcontrol)
Ask
Acquire
Appraise
Apply
Act & Assess
Patient
dilemma
Principles of
evidence-based
practice
Evidence alone does not
decide – combine with other
knowledge and values
Hierarchy
of evidence
Process of EBP
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EBM Sample ScenarioEBM Sample Scenario
• A 30 year old women came into your practice with a history of sore throat for 3 days. Upon physical examination you find slightly enlarged and injected tonsil and injected pharynx. She reported no significant past medical history. She asked you whether any medication can lessen the pain.
• You have seen a senior prescribing corticosteroid injection for such condition, and you wonder whether prescribing steroid in patient with acute sore throat works.
• You then search PubMed with keyword "Adrenal Cortex Hormones"[Mesh] AND "Pharyngitis"[Mesh] AND "Pain"[Mesh] and found a systematic review:
Systematic ReviewSystematic Review
• Corticosteroids for pain relief in sore throat: systematic review and meta-analysis